Evidence suggests that levodopa (the drug used to treat Parkinson's disease ) can reduce brain levels of SAMe. This depletion may contribute to the side effects of levodopa treatment, as well as the depression sometimes seen with Parkinson's disease. One study found that SAMe taken orally improved depression without changing the effectiveness of levodopa. However, it is also possible that over time taking extra SAMe could interfere with levodopa's effectiveness.
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All you need to know about SAMe(S-Adenosyl Methionine)